This project will investigate the association of the major histocompatibility complex (MHC) with autistic subjects in an area other than norther Utah. It will also study whether another gene, within the extended haplotype in proximity to the C4B gene of the MHC, rather than C4B itself, is primarily associated with autism. Further, it will explore for and against the possibility that immune deficiency is related to autism by allowing a pathogen or microorganism to persist and damage the brain or interfere with normal brain function. Finally, it will attempt to determine whether or not autoimmune processes are associated with the development of autism. Results may lead to a new treatment approach for autism.